double a,b,c,d,e,f,x,y,z,s,r;
main()
{
	for(;~scanf("%lf%lf%lf%lf%lf%lf",&a,&b,&c,&d,&e,&f);)
	{
		x=hypot(a-c,b-d);
		y=hypot(a-e,b-f);
		z=hypot(c-e,d-f);
		s=(x+y+z)/2;
		printf("%.2lf\n",2*3.141592653589793*x*y*z/(4*sqrt(s*(s-x)*(s-y)*(s-z))));
	}
}
